Commit a change of the composition: the LinkedIn accounts, the inbox packages, the credits a month, each part the whole new value (an omitted part stays). DANGEROUS: up to three Paddle calls, the decreases and free restorations first (nothing billed), then the credits top-up (a one-time charge), then the prorated LinkedIn and added packages, so a refused card stops only the last step (409 payment_declined). Call preview_billing_subscription_change first. Removing every line is a cancel (409 use_cancel); a pool below the sum of its shares is refused (409 allocated_exceeds_pool: lower the shares first; a standard account's one share follows the plan down); a credits change while a top-up is unpaid is 409 change_pending; an invoiced subscription is not re-priced here. The renewal date never moves. Owner only.

Contract:

• MCP tool change_billing_subscription, registry package mcp.id/billing_subscriptions, mount id.billing.
• Operation action, response envelope action.
• Flags: dangerous: the MCP layer gates it behind a preview/commit token, and the effect cannot be undone through this API.